We propose to continue the Carolina Breast Cancer Study, a population- based, case-control study that integrates molecular biology and epidemiology in the search for causes of breast cancer. Participants will include 20-74-year-old women residing in a 24-county area of central and eastern North Carolina. Cases will be women diagnosed with invasive or in situ breast cancer for the first time between 9/1/95 and 3/31/00. Comparison subjects will be frequency-matched to cases by sex, race, and age +/-5 years) and will be identified using computerized lists from the North Carolina Division of Motor Vehicles for women 20-64 years old and from the U.S. Health Care Financing Administration for women 65-74 years old. By the end of the funding cycle, data from 1600 women with invasive breast cancer and an equal number of appropriate controls will be available. Sampling will insure that approximately 50% of cases and controls are African-American. Information on established and hypothesized breast cancer risk factors will be obtained by personal interview. Blood samples for extraction of germline DNA will be collected from all consenting participants, and paraffin-embedded tumor specimens will be requested for all breast cancer cases. Medical records will be obtained to document treatment, stage, and prognostic characteristics to supplement descriptions available from pathology review of H&E slides of the breast tumor. The epidemiologic and clinical data and biological specimens will provide the basic resources necessary to address the relative contributions of genes and environment to breast carcinogenesis. The scientific questions of particular interest in this proposal are: 1) to what extent inherited susceptibility to breast cancer at various loci (BRCA1, BRCA2, MSH2) contributes to breast cancer, whether somatic alterations at the same loci are involved in sporadic disease, and which environmental/behavioral factors influence penetrance/somatic occurrence of the disease mutations; 2) whether specific, somatic, molecular alterations (amplification of HER-2/neu, PRAD1/EMS1, c-MYC, or 20q, p53 alterations, LOH at 17q21) can serve as signatures for etiologically- distinct subsets of breast cancer, and if so, which environmental,behavioral exposures increase risk of their occurrence; 3) whether specific alleles at P450 or other metabolic loci modulate effects of environmental exposures on breast cancer risk; and 4) whether racial differences in breast cancer among African-American and Caucasian women can be explained by specific molecular alterations or constellations of risk factors. In addition, the Carolina Breast Cancer Study is structured to facilitate implementation of other current and proposed projects, including studies on the HaRAS VNTR, on carcinoma in situ on fatty acids and breast cancer risk, on the role of pesticides, occupational cadmium exposure, and electromagnetic fields in breast carcinogenesis, and on the development of a genetic testing protocol for BRCA1.